Study of RuO4 decomposition in dry and moist air

Abstract

During a hypothetical severe nuclear accident on a pressurized water reactor (PWR), it is of primary importance to assess potential radionuclide release into the environment, and thus to better understand the volatile ruthenium tetroxide stability, in the containment building, due to its high radiotoxicity. The stability of RuO4(g) in dry and moist air, under conditions representative of a PWR containment building, is investigated. RuO4 decomposition occurs in bulk gas phase, without any specific affinity with surfaces. The kinetic rate law of RuO4 reduction is found to be dependent on the presence of steam. The humidity seems to play a catalytic role, as well as the presence of ruthenium dioxide deposits. The temperature is also a key parameter. In the presence of steam, the half-life times of RuO[4] are found to be respectively of 5 h and 9 h at 90 °C and 40 °C. A chemical reaction scheme consistent with the experimental observations is proposed.